Answered by Shaykh Faraz Rabbani
What if one only realises the time for suhur has expired but after a few minutes stated on the timetable? or finds one self on the actual time of expiry? in both cases is not sure if one has consumed actual trace of the food from inside the mouth that was stuck between the teeth, in that time? How does one distinguish between mere taste and actual trace of the food?

Walaikum assalam,
If you mistakenly consumed something after fajr time comes in, your fast is invalid. However, it remains wajib for you to refrain from eating, drinking and sexual intercourse and its like. This is something many people are unaware of, but is clearly mentioned in Hanafi texts. [Maraqi al-Falah, Hashiya Ibn Abidin, etc.]
If you are not sure that you have swallowed anything, then your fast remains valid.
Wassalam,
Faraz.